[Qemu-devel] Re: [PATCH 16/23] pci: pcie host and mmcfg support.

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Oct 05, 2009 at 07:06:56PM +0900, Isaku Yamahata wrote:
> @@ -1052,9 +1242,10 @@ PCIDevice *pci_create_simple(PCIBus *bus, int devfn, const char *name)
>  
>  static int pci_find_space(PCIDevice *pdev, uint8_t size)
>  {
> +    int config_size = pcie_config_size(pdev);
>      int offset = PCI_CONFIG_HEADER_SIZE;
>      int i;
> -    for (i = PCI_CONFIG_HEADER_SIZE; i < PCI_CONFIG_SPACE_SIZE; ++i)
> +    for (i = PCI_CONFIG_HEADER_SIZE; i < config_size; ++i)
>          if (pdev->used[i])
>              offset = i + 1;
>          else if (i - offset + 1 == size)
> diff --git a/hw/pci.h b/hw/pci.h
> index 00f2b78..1f402d2 100644
> --- a/hw/pci.h
> +++ b/hw/pci.h
> @@ -175,20 +175,26 @@ enum {
>      QEMU_PCI_CAP_MSIX = 0x1,
>  };
>  
> +/* Size of the standart PCIe config space: 4KB */
> +#define PCIE_CONFIG_SPACE_SIZE  0x1000
> +#define PCIE_EXT_CONFIG_SPACE_SIZE                      \
> +    (PCIE_CONFIG_SPACE_SIZE - PCI_CONFIG_SPACE_SIZE)
> +
>  struct PCIDevice {
>      DeviceState qdev;
> +
>      /* PCI config space */
> -    uint8_t config[PCI_CONFIG_SPACE_SIZE];
> +    uint8_t *config;
>  
>      /* Used to enable config checks on load. Note that writeable bits are
>       * never checked even if set in cmask. */
> -    uint8_t cmask[PCI_CONFIG_SPACE_SIZE];
> +    uint8_t *cmask;
>  
>      /* Used to implement R/W bytes */
> -    uint8_t wmask[PCI_CONFIG_SPACE_SIZE];
> +    uint8_t *wmask;
>  
>      /* Used to allocate config space for capabilities. */
> -    uint8_t used[PCI_CONFIG_SPACE_SIZE];
> +    uint8_t *used;
>  
>      /* the following fields are read only */
>      PCIBus *bus;


So I thought about this some more, and I think that this change
in unnecessary. PCI Express adds support for extended 4K
configuration space, but the only thing that must reside
there is the optional advanced error reporting capability,
which I don't think we'll need to implement, ever.

Everything else can reside in the first 256 bytes, just as for regular
PCI. And pci code already returns 0 for accesses outside the first 256
bytes, so express specific code is necessary.

If we do this, we can keep memcpy for the full original
space (it's just 4 cache lines) and simple memcmp
with no overlap checks will be enough to figure out
if something changed. To make that also possible for
bridges, we'll then just put the orig array inside
PCIDevice. Not sure I explain this last point clearly -
would you like to see a patch?

-- 
MST